The present invention relates to a composition of nanoplates and nanotubes wherein at least a portion of the nanoplates have at least one nanotube interspersed between two nanoplates. In particular, is described the exfoliation and dispersion of carbon nanotubes and graphene structures resulting in high aspect ratio, surface-modified carbon nanotube/graphene compositions that are readily dispersed in various media. Graphene structures here is meant to include graphene and oxygenated graphene structures. The carbon nanotubes here is meant to include carbon nanotubes and oxidized carbon nanotubes. The oxygenated structures of carbon nanotubes or graphene include, but are not limited to, carboxylic acid, amide, glycidyl and hydroxyl groups attached to the carbon surface.
These nanoplate-nanotube mixtures can be further modified by surface active or modifying agents. This invention also relates to nanoplate-nanotube composites with materials such as elastomers, thermosets, thermoplastics, ceramics and electroactive or photoactive materials. The graphene-carbon nanotube compositions are also useful as catalysts for chemical reactions. Also, the present invention pertains to methods for production of such composites in high yield.
Carbon nanotubes in their solid state are currently produced as agglomerated nanotube bundles in a mixture of chiral or non-chiral forms. Various methods have been developed to debundle or disentangle carbon nanotubes in solution. For example, carbon nanotubes may be shortened extensively by aggressive oxidative means and then dispersed as individual nanotubes in dilute solution. These tubes have low aspect ratios not suitable for high strength composite materials. Carbon nanotubes may also be dispersed in very dilute solution as individuals by sonication in the presence of a surfactant. Illustrative surfactants used for dispersing carbon nanotubes in solution include, for example, sodium dodecyl sulfate and PLURONICS. In some instances, solutions of individualized carbon nanotubes may be prepared from polymer-wrapped carbon nanotubes. Individualized single-wall carbon nanotube solutions have also been prepared in very dilute solutions using polysaccharides, polypeptides, water-soluble polymers, nucleic acids, DNA, polynucleotides, polyimides, and polyvinylpyrrolidone. The dilution ranges are often in the mg/liter ranges and not suitable for commercial usage.
If graphene is exfoliated, i.e., with the individual plates separated rather than stacked, in medium such as water, the thermodynamic energies due to incompatibility and the very high surface area of the graphene results in the plates recombining, and the plates become very difficult to separate into individual plates. Likewise, if graphene plates are to be oxidized, if the plates are bundled, then only the edges of the graphene are readily accessible for reaction.
In the present invention, discrete tubes ranging in diameter from a nanometer to 100 nanometers can be inserted between inorganic plates. In particular, carbon nanotubes can be inserted between graphene plates thus restricting their agglomeration and facilitating exfoliation in a broad range of materials including liquids and solids. Furthermore, as the plates are now separated, reactions can be entertained at the surface of the graphene plates to give, for example, oxygenated graphene structures. The diameter of the tubes can be used to control the inter plate distance. Selecting tubes of different diameters can lead to controlled transport of molecules or ions between the plates.
In view of the foregoing, nanoplate-discrete nanotube compositions and methods for obtaining them are of considerable interest in the art. A number of uses for discrete nanotube/single inorganic plates, particularly carbon nanotube/graphene compositions, are proposed including, for example, energy storage devices (e.g., ultracapacitors, supercapacitors and batteries), field emitters, conductive films, conductive wires, photoactive materials, drug delivery and membrane filters. Use of discrete carbon nanotube/graphene compositions as a reinforcing agent in material composites is another area which is predicted to have significant utility. Materials include, for example, polymers, ceramics, rubbers, cements. Applications include tires, adhesives, and engineered structures such as windblades, aircraft and the like.